Fig. 1. (a) Schematic of the TERS system. 4-Q PD, 4-quadrant photodiode; WPV, zero-order vortex half-wave retarder plate; BS, beam splitter. (b) Schematic of the virtual SP probe-excited TERS on a gold film. RP beam indicates the radially polarized incident beam.

Fig. 2. Numerical calculation of the electric field normalized to the traditional tightly focused electric field. (a) Schematic of the tip on glass. (b) Calculated electric field |E|2 distribution of the gold-coated tip apex on glass substrate excited by a tightly focused radially polarized 632.8 nm laser. (c) Profiles of the electric field |E|2 along the line through the center plane of the gap volume. (d) Schematic of the tip on gold film. (e) Calculated electric field |E|2 distribution of the gold-coated tip apex on gold film. (f) Profiles of the electric field |E|2 with different gold coating thicknesses. The yellow dashed lines denote the surface of the substrate and the tip apex. Axes units in (b) and (e): nm.

Fig. 3. (a) SEM image of the gold-coated AFM tip with a thickness of 60 nm; (b) Raman spectra of self-assembled 4-MBA layer measured when the tip was in the engaged mode (red curve) and withdrawn (black curve) mode; (c) spectral measurements on glass substrate with (red curve) and without (black curve) the metallic tip; incident laser, 632.8 nm, ∼1.8  mW; integration time, 1 s.

Fig. 4. (a) AFM image of SWCNT bundles deposited on the gold film; (b) height profile along the white dashed line in (a); (c) TERS signal along the dashed line in (a) at the Raman peak of the G-band at 1590  cm−1; (d) Raman spectra at positions A and B denoted in (a); laser power, ∼1.8  mW; integration time, 1 s.

Fig. 5. (a) AFM image of SWCNT bundles deposited on the gold film; (b) TERS imaging at the Raman peak of 1590  cm−1 according to the white dashed region in (a); laser power, ∼1.8  mW; integration time, 1 s.